These "C128" or 128 Hertz American made tuning forks are for vibration testing. They are weighted and individually tuned to the right frequency. The best in the world. Each fork has been carefully hand smoothed so that there are no sharp edges. If you have seen 128 Hertz extra-long tuning forks without weights at the ends, then you have seen the "student grade". These are the professional grade, and they are of the highest-quality proprietary aluminum alloy. A complete set of these forks can be seen in the Smithsonian in Washington D.C. We weren't bluffing about them being the best in the world. These, the 128 Hertz variety, weigh approximately 3.3 ounces each.

Also see the C256 or 256 Hertz weighted fork which is used for vibration as well as hearing testing, and the C512 or 512 Hertz fork, which is an unweighted fork used only for hearing testing.